Circuit breaker thermal and magnetic tripping mechanism



Dec. 30; 1969 F. E. MYERS ETAL 3,487,343

CIRCUIT BREAKER THERMAL AND MAGNETIC TRIPPING MECHANISM Filed Dec. 21, 1967 2 Sheets-Sheet l INVENTORS' F62 //l E. NYE/P3 11/5570 K- 6000M Dec. 30, 1969 v F. E. MYERS ET AL 3,487,343

CIRCUIT BREAKER THERMAL AND MAGNETIC TRIPPING MECHANISM Filed Dec. 21, 1967 2 Sheets-Sheet 2 PF/OR I91? 7' fig 202 ,r/fl/ in! za/z w A a I r? y! w I 1 INVENTORS fZ-Y/J f. MFA-36.5 W557? M 6000/00 United States Patent Ofiice 3,487,343 Patented Dec. 30, 1969 US. Cl. 335-35 4 Claims ABSTRACT OF THE DISCLOSURE A circuit breaker thermal and magnetic tripping mechanism comprising a bimetallic strip which deflects responsive to temperature variations, one end of the strip being pivotally mounted and the other end being adjacent an abutment, whereby as the temperature, e.g., increases and the strip deflects, its latter end abuts the abutment and the strip bows and pivots around its pivotally mounted end; a circuit breaker tripper latch connected with the bimetallic strip in the vicinity of its pivotally mounted end; a circuit breaker contact tripper which causes tripping open of the breaker contacts, the tripper being supported by the latch to prevent tripping open of the contacts; deflection of the strip drawing the latch away from its supporting position with respect to the tripper, thereby permitting tripping of the circuit breaker; a magnetizable element in engagement with the latch which becomes magnetized by a high fault current; the magnetized element being drawn toward an armature which draws the latch away from its supporting position with respect to the tripper, thereby causing tripping of the circuit breaker contacts.

This invention relates to an electric circuit breaker tripping mechanism and more particularly to a combined thermal and magnetic tripping mechanism and to a thermal tripping mechanism.

In recent years there has been considerable eflort expended in the electrical industry to reduce the size of circuit protective equipment. For example, in the area of small air circuit breakers of the type with which the instant invention is intended to cooperate, there has been industry acceptance of one-half inch wide circuit breakers as a substitute for the long accepted one inch wide breaker. Further evidence of the present emphasis on reduction in size and simplicity in design is evidenced by U.S. patent application Ser. No. 587,709 (C1253 SCB) filed Oct. 19, 1966, entitled Circuit Breaker Resetting and Closing Mechanism, and assigned to the assignee of the instant invention, where there has been described in great detail a novel circuit breaker which has achieved utmost simplicity in design and maximum reduction in overall size.

Simultaneously with the development of smaller and more simplified circuit breakers, engineers have sought ways of minimizing the size of circuit breaker tripping mechanisms, while maximizing their operating capabilities. Since a tripping mechanism for a circuit breaker usually must move in some manner to initiate tripping open of the breaker contacts, it must be large enough to be able to move sufliciently to cause tripping.

Prior art thermal tripping mechanisms usually employ a bimetallic strip which is fixedly mounted at one end, and which is free at its other end to deflect in response to temperature variations. A latch or other means for initiating tripping of the circuit breaker is connected to the bimetallic strip as close as possible to its free end to maximize the distance the latch moves due to deflection of the bimetallic strip.

In the present invention, in order to obtain maximum movement of the latch or other circuit breaker tripper operator, the thermal element, which may be a bimetallic strip, is not fixedly, but is pivotally, mounted at one end. The thermal element deflects in a first direction as a result of temperature variations, e.g., temperature increases, u on the occurrence of which it is desired that the tripping mechanism operate. A fixed abutment is provided which is constantly engaged by the free end of the thermal element, thereby preventing deflection of the free end. The thermal element is normally biased by a biasing means or spring so that the free end of the element is in engagement with the abutment. The thermal element bows instead and as it bows to an increasing extent, since its end adjacent the abutment cannot deflect, its pivotally mounted end pivots about its pivotal mounting.

As a further feature the position of the abutment may be made adjustable to any of a variety of predetermined positions to calibrate the latch bite, or distance the latch must slide due to deflection of the overload responsive element, before the circuit breaker is tripped. An additional advantage of the present invention over the prior art is that calibration of the latch bite at the lower extremity of the thermal element is more direct and less critical than calibrating steps required in the prior art. Another advantage is that instantaneous and interpole (if the present invention is used in conjunction with a multiphase device) trip operations may be accomplished without detrimental thermal element interference.

A circuit breaker has a pair of contacts, one of which is relatively movable with respect to the other, and has a tripper for the contacts which is caused, by appropriate movement of the tripping mechanism, to separate the relatively movable contact from the relatively stationary one. The tripper is normally blocked from tripping open the circuit breaker contacts by a blocking element, such as a latch, which is connected to and operated by the tripping mechanism.

In the present invention, a latch is provided that engages a latch member on the circuit breaker tripper cradle, which is more fully described below. The latch is connected with the thermal element, and is positioned in opposed relationship to what is the concave side of the thermal element when it bows. As the thermal element hows, the latch moves along with the bowing portion thereof, thereby permitting the tripper to operate. Consequently the latch serves as a trip initiator for the tripper. It is within the contemplation of the invention to position the latch in opposed relationship to the convex side of the bowing thermal element, since it will be caused to move regardless of which side it is on and it is the movement of the latch which causes tripping.

The latch may be connected to the thermal element at its pivotally mounted end. As that end of the thermal element rotates around its pivotal mounting, the latch is caused to rotate around the pivotal mounting. The latch is supported on a shaft extending away from the point at which the latch shaft is connected to the thermal element, whereby the rotation of the end of the thermal element operates through the latch shaft to cause the latch itself to rotate a considerable distance upon deflection of the thermal element.

The above described thermal tripping mechanism is readily adapted to serve also as a magnetic tripping mechanism by providing a magnetizable element in engagement with the latch or latch shaft. A stationary armature of steel or other material which attracts magnetized items is positioned near the magnetizable element. In the event of a high fault current, the magnetizable element is magnetized and is drawn toward the armature drawing the latch along with it, thereby causing tripping of the circuit breaker.

A thermal and a combined thermal and magnetic tripping mechanism can be placed in any circuit breaker or in any other electrical device, which employs an element that is moved by a deflecting thermal element, such as a bimetallic strip.

Accordingly, it is an object of the present invention to provide a circuit breaker thermal and magnetic tripping mechanism which is of minimium size.

It is another object of the present invention to provide such a thermal and magnetic tripping mechanism that moves sufliciently to initiate circuit breaker tripping.

It is another object of the present invention to provide a circuit breaker tripping mechanism having a thermal element which is pivotally mounted at one end thereof and to which end of the thermal element is also mounted the trip initiator, thereby maximizing movement of the initiator.

These and other objects of the present invention will become apparent when the following description is considered in conjunction with the accompanying drawings, in which:

FIGURE 1 is a plan view, with the cover removed, of a circuit breaker in the on position containing the thermal and magnetic tripping mechanism of the instant invention;

FIGURE 2 is a fragmentary view of the circuit breaker of FIGURE 1 showing the tripping mechanism of the instant invention immediately after it has initiated tripping of the circuit breaker;

FIGURE 3 is a perspective fragmentary view of the circuit breaker of FIGURE 1, showing the tripping mechanism of the instant invention, with the circuit breaker in the on position;

FIGURE 4 illustrates the effect of employing a prior art thermal element; and

FIGURE 5 illustrates the effect of employing a thermal element in accordance with the teachings of the instant invention.

Referring to FIGURE 1, there is shown the internal mechanism of a circuit breaker containing the tripping mechanism of the instant invention. It is re-emphasized that although the circuit breaker tripping mechanism 60 of the instant invention will be specifically described with respect to the internal mechanism 10 shown in application Ser. No. 587,709 now Patent No. 3,377,574, such disclosure is intended in no way to limit the application of the instant invention, since the instant invention is equally applicable to any circuit breaker mechanism and to any electrical device.

Similarly, it is to be understood that although the instant invention will be described with respect to a circuit breaker for the protection of a single phase of current, the instant invention can be readily employed in a multi-phase breaker, e.g., by using a common trip bar to join the hereinbelow described pivotable supports 65 in every phase of a multi-phase circuit breaker.

The circuit breaker mechanism 10 includes the common mounting plate 11, which is integrally provided with the following parts, an upstanding cradle pivoting tab 12, an upstanding relatch mechanism pivoting tab 13; an upstanding tripper mechanism pivoting tab 15; and an upstanding spring retaining tab 16. In addition, plate 11 includes a generally centrally located operating handle pivoting aperture 17 and an arcuate slot 18, which receives an upstanding tab portion 23 of the operating handle 20, as hereinafter described.

The operating handle 20 of the circuit breaker includes an upstanding knob receiving tab 21 at one end thereof and a pair of upstanding tabs 22 and 23 at the opposite end thereof. Tab 22 is positioned in aperture 17 and serves as a pivot about which operating handle 20 may experience rotation in a plane parallel to the plane of mounting plate 11. Tab 23 of handle 20 is freely received within arcuate slot 18 and extends forward of mounting plate 11 when operating handle 20' is placed behind plate 11 with tab 22 in aperture 17. Biasing means in the form of spring 26 is secured at one end thereof to tab 23 and at the opposite end thereof to the upstanding spring-retaining tab 16 so as to constantly bias the operating handle 20 in a counterclockwise direction, in FIGURE 1, about the pivot defined by tab 22.

A cradle 30 is provided having an end 31 which receives in aperture 32 the cradle pivoting tab 12 of mounting plate 11. The opposite end of the cradle 30 includes an upstanding latch tip 34 which cooperates with the latch 75 of the tripping mechanism 60, as will be described in further detail. Intermediate the ends of cradle 30 is an overturned tab 35 which cooperates with an open-ended slot 41 in movable contact arm to provide a pivot 42 for arm 40.

The opposite end of movable contact arm 40 integrally carries a spring-retaining portion 44 and a portion 45 which carries movable contact pad 46 thereon.

Disposed opposite movable contact pad 46 is stationary contact pad 47 secured to the stationary st-ab terminal 48 of the breaker. The contact pads 46 and 47 comprise the cooperating contacts in the breaker.

Cradle 30, when released by hereinbelow described latch 75, coacts with contact arm 40, later described spring 49 and handle 20 to cause the cooperating contacts to be separated and thus trips open the circuit breaker, whereby the cradle and the elements coacting with it serve as the tripper.

A main operating spring 49 is secured at one end thereof to the spring-retaining portion 44 and at the opposite end thereof to a spring-retaining portion 27 which is an integral portion of the upstanding kno retaining portion 21 of the operating handle 20.

Current flow in the circuit breaker is through the path defined by sta'b terminal 48, stationary contact pad 47, movable contact pad 46, conductive braid 51, hereinbelow further described thermal element 61, conductive braid 52 and stab terminal 53.

The tripping mechanism of the present invention will be described in detail below. Its function is to initiate tripping apart of movable contact 46 and stationary contact 47.

The circuit breaker shown in FIGURE 1 also contains an automatic relatching mechanism which is more fully described in co-pending patent application Ser. No. 587,709, now Patent No. 3,377,574. Since the present invention is directed toward a tripping mechanism for a circuit breaker, a description of a relatching mechanism is omitted.

Tripping mechanism 60 is a combined thermal and magnetic tripping mechanism. The present invention could be applied with equal facility alone to a thermal tripping mechanism. Referring to FIGURES 13, the thermal tripping mechanism comprises a thermal element 61, which has the characteristics of deflecting as a result of variations in temperature. The temperature variations to which thermal element 61 is to respond may be variations in ambient temperature within the circuit breaker trip unit, or may be temperature variations due to variations in the current load passing through the circuit being protected. The thermal element may itself be connected into the circuit being protected, or may be positioned adjacent a heater which is connected into the circuit being protected. If the thermal element is to respond to ambient temperature changes, then it would be positioned away from the circuit being protected to avoid its being affected by the temperature of elements in the circuit.

The most common deflecting thermal element is a bimetallic strip, comprised of two face-bonded strips of metal, having different coeflicients of expansion. End 62 of thermal element 61 is free to pivot away from the end of abutment 70, to be described, so that magnetically caused tripping of the breaker can occur. End 63 of thermal element 61, on the other hand, is fixedly mounted to a support 65. Support 65 has an aperture 66 in which is positioned tripping mechanism pivot tab 15. Support 65, and hence thermal element 61 are, therefore, pivotally mounted on tab 15. The manner in which pivoting occurs is described below.

As element 61 is subjected to temperature variations to which it is desired that element 61 respond, e.g., to increase in temperature, it will bow, as shown in FIGURE 2. Normally, end 62 of element 61 would move in a counterclockwise direction, as viewed in FIGURE 2, thereby making the side 64 of element 61 concave, while the side 64 thereof becomes convex. However, the present invention contemplates the placement of an abutment 70 in the path of movement of end 62 of element 61. Abutment 70 consists of upraised tab 71, which is attached to mounting plate 11 and through which is passed the abutting element 72. Element 72 may be a screw which is passed through a threaded aperture in tab 71. The screw 72 is adjustable to any of a variety of predetermined positions to calibrate the latch bite of the circuit breaker by adjusting the initial position of the end 62 of element 61. The thermal element 61 is secured to support 65 as is the latch 75, to be described. By spring 80, latch 75 and thus support 65 and element 61 are biased counterclockwise in FIGURE 1, to keep latch 75 in engagement with latch tip 34. If screw 72, for example, is rotated so that its free end moves to the right, spring 80 will hold end 62 of element 61 in engagement with screw 72 and element 61, support 65 and latch 75 will pivot counterclockwise, thereby increasing latch ibite, i.e., the length of latch 75 that extends over latch tip 34. Latch bite, it is apparent, may be decreased by rotating screw 72 so that its free end will move left.

A circuit breaker trip initiator, viz latch 75, is provided which serves as the element that initiates tripping open of the contacts. The latch 7 5, as can be seen in FIGURES 1 and 3, is normally positioned where it blocks latch tip 34 of cradle 30. Latch 75 is supported by shaft 76, which is attached to support 65 or to thermal element 61 in the vicinity of end 63 of thermal element 61.

Biasing tension spring 80 is provided which is connected by means of tab 81, either to latch support 76 or to hereinbelow described magnetizable armature 90 which is secured to latch support 76. Spring 80 is at its other end connected with relatch mechanism plate 82, more fully described in the aforementioned copending application. Spring 80 draws latch support 76 and latch 75 into a blocking position with respect to latch tip 34. Latch support 76 is drawn counterclockwise which, in turn, draws thermal element 61 and support 65 counterclockwise about pivot 15. This keeps end 62 of thermal element 61 in engagement with abutment 70.

A combined thermal and magnetic tripping mechanism requires a magnetic tripping mechanism. Magnetizable element 90 is provided. It is positioned in proximity to the circuit being protected, and is comprised of unmagnetized metal, such as steel, which is capable of becoming magnetized if a high fault current passes through the circuit. Armature 91 is provided, which is secured to resilient spring arm 92. Arm 92 is mounted to upturned tab 95 of mounting plate 11. Spring arm 92 biases armature 91 to the right, as viewed in FIGURE 1 against fixed stop 94, fixedly secured to the breaker casing. Armature 91 may freely move to the left away from stop 94, to permit overtravel of magnet 90 during both instantaneous and thermal tripping. Armature 91 is comprised of a material, such as steel, which attracts magnetized materials to it. The armature 90 is in engagement with the support 76 of latch 75.

The combined thermal and magnetic tripping mechanism of FIGURES l-3 initiates tripping of the circuit breaker of FIGURE 1 in the following manner. In the event of a time delay or low fault current passing through thermal element 61, or in the event of an undesirable ambient temperature existing in the circuit breaker housing, the thermal element 61 which is in its undeflected condition of FIGURES 1 and 3, begins to deflect and bow, as shown in FIGURE 2, because its end 62 is in engagement with abutment 70, the bowing of thermal element 61 causes thermal element support 65 to pivot clockwise about its pivot 15. Latch 75, connected by its support 76 either to thermal element support 65 or to end 63 of element 61, is also pivoted clockwise about pivot 15. When latch 75 has moved a suflicient distance (from its dotted line position in FIGURE 2 to its solid line position), it is removed from its blocking position with respect to latch tip 34, thereby enabling the circuit breaker to be tripped in a manner to be described below.

In the event of a high fault current, magnetizable armature will become magnetized and will be attracted to element '91. Armature 90 is connected with latch support 76, and as armature 90 is drawn toward element 91, it draws latch support 76 and latch 75 toward element 91, which causes latch support 76 and support 65 to pivot clockwise about pivot 15, and removes latch 75 from its blocking position with respect to latch tip 34, thereby permitting tripping of the circuit breaker in the manner decribed below.

Tripping occurs in the following manner.

In FIGURE 1, the circuit breaker is in the on position, i.e., with contact pads 46 and 47 completing the circuit path through the breaker. When a time delay, low or instantaneous fault current has been detected by tripping mechanism 60 so as to rotate latch 75 away from its blocking position with respect to latch tip 34, movable contact support arm 40 is still in the position of FIGURE 1. Spring 49 draws spring-retaining portion 44 toward spring retainer 27 and pulls pivot 42 of cradle 30 upward (in FIGURE 1), thus causing cradle 30, which is no longer restrained by latch 75 from clockwise rotation, to rotate clockwise. Spring-retainer 27, pivot 42 and portion 44 comprise a toggle and as spring 49 collapses and pulls up on portion 44, it causes the toggle to collapse to the right (as viewed in FIGURE 1), whereby the movable contact 46 wipes over stationary contact 47. A kicker projection 30a is provided on cradle 30, and after cradle 30 has rotated clockwise a distance, projection 30a strikes movable contact support arm 40, and the impact separates movable contact 46 from stationary contact 47, and rotates movable contact support arm 40 about pivot point 42.

As cradle 30 rotates, when point 42 passes to the right (as viewed in FIGURE 1) of the force line of spring 49, the toggle formed by spring-retainer 27, point 42 and portion 44 collapses to the left completing contact separation. (For greater detail concerning separation of the contacts of the circuit breaker of FIGURE 1, see copending application Ser. No. 632,045, filed Apr. 19, 1967 by Carl E. Gryctko, entitled Circuit Breaker Mechanism Mounting Plate Assembly, and assigned to the assignee of the instant invention.)

There has just been described a novel combined thermal and magnetic tripping mechanism, and a novel thermal tripping mechanism, which comprises a thermal element to one end of which is connected a latch which operates to initiate circuit breaker contact separation. The thermal element is pivotally mounted at one end, and engages an abutment at its other end, whereby as the thermal element deflects due .to temperature variations, the pivotally mounted end of the thermal element pivots and the latch supported from the pivotally mounted end also pivots out of engagement with the latch tip of the circuit breaker tripper, thereby initiating circuit breaker tripping. A magnetizable element is connected with the support for the latch, and in the event of a high fault current, the now magnetized element is drawn toward an armature, thereby drawing the latch out of engagement with the latch tip of the tripper, which initiates circuit interruption.

The pivotally mounted thermal element of the instant invention is an improvement over the prior art. Referring to FIGURE 4, which illustrates prior art mounting of thermal elements, the thermal element 101 is fixedly mounted or cantilevered to its support 102 at its end 103. The free end 105 of thermal element 101 can deflect without obstruction. A latch 105 is provided which is connected to the thermal element as near to the free or unmounted end 104 as possible, since it is end 104 that has maximum deflection due to variations in temperature. The thermal element 101 is arranged to deflect clockwise to operate latch 105 toward the left, as viewed in FIGURE 4.

Using bimetal 101, for a predetermined variation in temperature, latch 105 moves a distance A from its dotted line to its solid line position. While element 101 is deflecting, end 106 of latch 105 is rotating clockwise through an arc of x".

Referring to FIGURE. 5, a thermal element 201 having identical deflection characteristics to thermal element 101 is provided. It is fixedly mounted to support 202, which is, in turn, pivotally mounted on pivot 15. The length of thermal element 201 from its end 203 to its end 204 is identical to the length of prior art element 101 between its ends 103 and 104. Latch 205 is provided having end 206. Latch 205 is supported by latch support 207 which is fixedly attached at its end 208 to support 202. Thermal element 201 is positioned to deflect counterclockwise, as viewed in FIGURE 5, except that its end 204 engages abutment screw 72, and is unable to move counterclockwise. As the temperature varies, thermal element 201 bows. An identical temperature variation, as was impressed upon element 101, is impressed upon element 201. As element 201 bows, it causes support 202 to pivot around pivot 15, thereby causing latch 205 and its support 207 to move from the dotted line position in FIGURE to the solid line position. End 206 of latch 205 has moved a distance B during the pivoting of support 202. Distance B is greater than distance A, whereby the object of the present invention is realized. In addition, end 206 has rotated clockwise, e.g. y, which is a smaller angle than x rotation of end 106 of latch 105. The decrease in the clockwise rotation and, hence, in the downward movement of latch 205 as compared to the downward movement of latch 105 has the following beneficial advantage. As the latch moves downward, it moves the latch tip 34 and cradle 30, shown in FIGURE 1, in a counterclockwise direction, thereby necessitating that cradle 30 travel a greater distance before completing circuit interruption. The present invention reduces the extra distance that must he traveled by the latch tip 34 and cradle 30.

In the fixedly mounted cantilever type thermal element of FIGURE 4, With the latch connected to the thermal element, the deflection at the latch is proportional to the square of the distance between the latch 105 and the support 102. In the embodiment of FIGURE 5, with the same deflection as in that of FIGURE 4 at the extreme ends of the thermal element, the deflection at the latch 205 is proportional to the first power of the distance between latch 205 and support 202, because the thermal element deflection has been converted into rotation. Comparing the two types of construction shown, it may be seen that the embodiment of FIGURE 5 results in approximately one and one-third times the deflection at the latch, as the common cantilever type. The advantage of the system of the invention increases in proportion to increases in the ratio of the distance from the support 202 to the latch 205 to the distance from support 202 to the end 204 of the bimetal in engagement with the abutment 72. Note also that in the embodiment of FIGURE 5, the moment at the thermal element support 202 due to the force being exerted on the latch at cradle 30 remains at a constant value about pivot 15 throughout the tripping motion of support 202. In the case of the cantilevered thermal element 101 of FIGURE 4,

with its rigid support, the moment increases as the thermal element moves, resulting in a possible increasing rotation toward the cradle, and thus toward the latched position, thereby requiring deflection to a greater extent of element 101 to trip the circuit breaker.

Although there has been described a preferred embodiment of this novel invention, many variations and modifications will now be apparent to those skilled in the art. Therefore, this invention is to be limited, not by the specific disclosure herein, but only by the appending claims.

The embodiment of the invention in which an exclusive privilege or property is claimed are defined as follows:

1. In a thermal trip mechanism for a circuit breaker;

said circuit breaker comprising a pair of cooperating contacts, one of which is movable relative to the other, and comprising a tripper for causing separation of said relatively movable contact from the other of said contacts;

said tripper being movable to a first position wherein said contacts are in engagement and to a second position wherein said contacts are out of engagement;

a latch for said tripper;

said latch being connected to a trip mechanism such that said trip mechanism, when actuated, causes said latch to cause said tripper to move to said second position;

said trip mechanism comprising a thermal element which deflects in a first direction due to temperature increase; said thermal element having a first end and a second end; said circuit breaker having a fixed support for said thermal element first end and said thermal element first end being connected with said support therefor;

said circuit breaker including an abutment for said second end of said thermal element; said abutment being positioned to be engaged by said second end of said thermal element once the thermal element deflects in said first direction;

the improvement comprising,

said latch'including a rigid nondeflecting support portion which is operatively connected to move wit-h said thermal element and which is connected with said thermal element support in the vicinity of said first end of said thermal element;

said latch having an operative portion located away from said thermal element support, which portion is adapted to be engaged with said circuit breaker trip mechanism; said latch being positioned with respect to said thermal element so that the operative portion thereof is located to be in opposed relationship to and facing away from the side of said thermal element which faces toward said first direction; said thermal element being pivotable about a fixed pivot therefor as it deflects due to temperature increase and its second end engages said abutment;

said latch operative portion being so conected with said thermal element first end as to pivot with said thermal element first end as the latter pivots around said support therefor when said thermal element deflects.

2. In the thermal trip mechanism of claim 1, the improvement further comprising,

said abutment comprising an adjustable element which is adjustable to position said second end of said thermal element in any of a variety of predetermined positions while said thermal element is deflecting and said second end is in engagement with said abutment.

3. A thermal and magnetic circuit breaker trip mechanism comprising, in combination,

the thermal trip mechanism of claim 1; and

a magnetic trip mechanism comprising,

9 10 a magnetizable armature in engagement with said References Cited latch and in proximity to the circuit being protected, whereby in the event of a high fault current, said UNITED STATES PATENTS magnetizable armature will become magnetized by 2,360,684 10/1944 f g 33535 the magnetic field in the vicinity of the circuit being 2,425983 8/1947 Blngenhelmer 335-37 protected; 5 2,677,026 4/1954 Bingenheimer 335 37 a fixedly mounted element positioned near said mag- 2,786,917 3/1957 Casey 33537 netizable armature, whereby when said armature is FOREIGN PATENTS magnetized, it is attracted toward said element,

thereby moving said latch toward said element, caus- 10 137072 5/1950 Australia ing said tripper to initiate contact separation. 4. In the thermal and magnetic circuit breaker trip BERNARD GILHEANY Pnmary Exammer mechanism of claim 3, H. BROOME, Assistant Examiner the improvement further comprising, said element being positioned to draw said magnetizable 15 armature in a direction opposite said first direction. 337-74 US. Cl. X.R. 

